This invention relates to computer and environmental systems, and more particularly relates to power shedding during extended power outages.
Uninterruptible power supplies (UPS) are known which provide power to equipment such as computer and telephone equipment during power grid outages. These devices include an auxiliary source of power, such as a battery, which charges while the power grid is in operation, and which provides power to the computer or other equipment during power outages. Being battery based, these devices have only a relatively lifted amount of power available before the computer or other devices must be shut down. Once the battery has discharged (total power failure), it is too late to shut down the computer or other equipment.
A UPS typically has several electronic devices connected thereto. For example, a computer, an associated printer, and an associated monitor may all be supplied power from a single UPS. It should be appreciated that some devices are more important than others in terms of the criticality of keeping them powered up during a power outage. Moreover, different devices have different power requirements, which can result in faster than necessary discharge of the UPS battery. However, the particular devices to be connected to a UPS cannot in general be known in advance, so it is difficult to build a UPS which will shed the desired loads at the desired times and in the desired order.
Many UPS devices include a set of output contacts which provide alarm signals, such as low battery alarms and power failure alarms. Software has been designed to monitor these alarms and use that information to perform a controlled shut down of the connected equipment. Thus, although it would be desirable to use these alarm contacts for other purposes, it is important that they be left for use of the existing software.
In certain circumstances, it is important that the selection and deselection of outlets be manually changeable, but this is not readily accomplished with reasonably priced UPSs. Moreover, some devices should not be restarted after a power outage without human intervention. Many available UPSs do not provide the ability to keep a device offline once power has been restored. Other devices require that a power shutdown cycle be completed before power is restored. This requirement is not achievable by many UPS units.